You can commit war crimes. You can be a Loan Shark. You can even kick puppies on vacation. But if you betray you are the lowest form of creature there is. If this attitude is described from the victim's point of view rather than as the expected attitude of neutral observers, it would be Et Tu, Brute?.
Note that this doesn't necessarily mean that the traitor is actually evil. A turncoat by definition only has their own advancement in mind, but someone who is a Defector from Decadence does so by turning on the obviously immoral team they previously worked for. This can even head into downright Moral Myopia with situations like gangsters treating people who work with the authorities as the scum of the earth for exposing their own criminal activities. Indeed, different interpretations of what constitutes loyalty and betrayal (and especially if one should remain loyal to an evil organization) make this a contentious issue in real life, at least if someone considers evil organizations worthy to content with. This is obviously an in-universe reaction and doesn't cover the author's and the audience's attitude towards it.
Sometimes Zig-Zagged or averted in Spy Fiction for fairly obvious reasons. Traitors from the good guy's team are evil, but traitors from the bad guy's team are sometimes sympathetic, depending on their motivation. In that case, it’s not the treachery itself, but the choice of sides that matters. When the enemy turns one of your own, it is more like Et Tu, Brute?. In war stories, it's why The Quisling and his fellow collaborators are even more despised than the actual occupiers.
The idea of Sacred Hospitality is big on this. It's perfectly fine to kill each other on the battlefield, but luring someone into your home with the promise of protection just so you can kill them is truly despicable. Someone who believes this may also hold the views embodied in My Master, Right or Wrong or My Country, Right or Wrong.
If even those who profit by the treachery treat the traitor this way, that is Rewarded as a Traitor Deserves. Unless they betray them for self-serving reasons, making them the treacherous ones. A villain who makes a point to defy this will insist that I Gave My Word. A Regretful Traitor is about the only type of betrayer who may remain sympathetic. See also The Oathbreaker for general cases of people breaking sworn promises, regardless of how they're treated for it.
- In Fate/Apocrypha, Avicebron switches sides to the Red Faction, on the condition no harm is to come to his master. Chiron initially believes this is because of Undying Loyalty. However, Avicebron proves him wrong by using said master as the magical core of his colossal golem. An infuriate Chiron, incensed at the depths he's sunk to complete his dream, shoots an arrow straight into his forehead. This act is considered so horrible that Avicebron in his Fate/Grand Order incarnation considers it one of the worst things he has done.
- The Runaways have a very clear policy on traitors: if you betray the team, Nico Minoru will tear your damn heart out. Given that its founder betrayed the team and nearly got them all killed, this policy is probably understandable.
- Deathstroke once rewarded Cheshire for selling out her own team by shooting her in the gut and leaving her for dead while noting his utter disgust with her actions.
- Don Bluth's Titan A.E. has the Plot Twist that The Hero's mentor, Captain Korso, sold him out to the Drej, convinced that humanity is "circling the drain." While Cale tries to appeal to any last shred of decency in Korso's heart, The Dragon informs them both that the Drej are rewarding him to eliminate both Cale and Korso, leaving zero surviving humans capable of activating the Titan. The Starscream gets his head unscrewed for his effort.
- The General's Daughter: The film combines this trope with Rape Is a Special Kind of Evil. A female officer, the eponymous General's daughter, is revealed to have endured a horrific gang rape from male soldiers while she was enrolled at West Point. The rape was already traumatizing, but she might have recovered from it until her father betraying her by covering the event up to get a promotion for himself broke her psyche completely. The investigator (played by John Travolta) ends up concluding that it was her father who really killed her and promises that he'll prosecute both him and the rapists for their crimes.
Brenner: Someone once asked me what's worse than rape. Now I know the answer. Betrayal.
- It's the Berserk Button for Doctor Ben Sobel in Analyze That, after seeing many actual crimes during two movies.
Ben: I can't take it anymore! That's what I hate about you fucking sociopaths! You just keep changing the rules to suit yourselves. Well, not this time, you anti-social asshole. You fucked with the wrong shrink!
- The traitors are purged in the climax of each movie of The Godfather Trilogy.
- A major theme in A Few Good Men where different moral codes and conceptions of treachery clash with each other.
- Colonel Jessep ordered the Code Red on the victim, Willy Santiago, because he tried to exchange incriminating information against a transfer, but then automatically sacrifices those who loyally apply that order.
- Lieutenant Kendrick candidly declares in court that the victim died because he has no honor and that Dawson once committed a crime by giving food to a punished man.
- Lieutenant-Colonel commits suicide because he can't bear his guilt and refuses to testify against his superior.
- After Judge Randolph orders Downey and Dawson to be dishonorably discharged from the Marine Corps, the latter concludes they indeed betrayed the victim and the principles they were supposed to defend as Marines.
- This is a central theme in I Shot Jesse James. Bob is cursed and spat upon by nearly everyone for shooting his longtime companion Jesse James in the back, even though James was a thief and murderer. It doesn’t help that people still aren’t quite willing to let go of their romanticized image of James as a Robin Hood-style rebel.
- Inferno, part 1 of Dante's The Divine Comedy. The Ninth Circle of Hell is a vast frozen lake in which traitors are entombed. In the center of it all is Lucifer himself, trapped up to his waist, his wings beating in a futile attempt to free himself, but the winds freezing the water. And his three heads are chewing on Brutus, Cassius, and Judas Iscariot.
- To clarify, the ninth circle is the lowest circle of hell (the highest contains virtuous pagans, good people who simply weren't baptized). Basically, according to Dante, there is no sin worse than betrayal.
- This viewpoint is common in Westeros, the main setting of A Song of Ice and Fire.
- Among many nasty feudal overlords, the houses Frey and Bolton stand out as the least likeable, because they are traitorous. The mercenary captain Vargo Hoat lost his chance of a political career in Westeros because of Values Dissonance: as a native of Essos, he thought switching sides is okay for him. It wasn't, and his former allies the Lannisters were particularly intolerant to this.
- One particular form of treachery is especially reviled in Westeros, namely violating Sacred Hospitality. The aforementioned House Frey became hated by all of Westeros because of that transgression (the victim was not just anyone, but their king, making it also high treason for a double whammy).
- Jaime Lannister, a knight of the Kingsguard, became famous for slaying King Aerys the Mad. From our perspective, that was a noble deed, especially considering the fact that the king planned to burn his capital down with all its citizens. However, as a member of the Kingsguard, Jaime swore to serve and protect his king, and, by killing him and saving countless lives, he committed a traitorous act. This made Jaime infamous and gave him the ignoble moniker of "The Kingslayer", even among former enemies of King Aerys.
- In the legend of the Rat Cook, a cook of the Night’s Watch killed the king’s son and served him to the king as dinner. He was then punished by the gods by being turned into a rat. However, he was not punished for murder or cannibalism, but for betraying his guest and breaking the Sacred Hospitality.
- In the Arcia Chronicles, treachery is treated as one of the worst sins: it is a treachery that sets in motion events that culminate in The End of the World as We Know It, and the resident Horsemen of the Apocalypse are reincarnations of four kings who betrayed their loyal subjects and friends during their lifetimes.
- In Reflections of Eterna (by the same author as Arcia Chronicles), betrayal often has massive supernatural consequences, such as the utter obliteration of the Nador Duchy by freak earthquakes after Richard Oakdell (the Duke of Nador) betrays his suzerain (and implied-to-be the rightful king) Roque Alva at a Kangaroo Court.
- Harry Potter:
- Rereading the third book after the seventh makes Snape's hatred of Sirius much clearer: In addition to his grudge against him from his schoolkid bullying, he, like everyone else, thought Sirius had betrayed the Potters to Voldemort, and thus was partly responsible for Lily's death.
- Taken slightly too far in the fourth book, where Ron considers Hermione dating Viktor Krum (the Durmstrang champion) as aiding the enemy to cover his jealousy (causing a Broken Pedestal moment, as he'd been a big fan of Krum's up to then). Hermione doesn't see what the big deal is, but then she also doesn't get why Quidditch is seen as a good thing when all it does is cause tension and resentment between Houses (she's not wrong, but as the viewpoint character is a Quidditch player...).
- Peter Pettigrew is on the receiving end from both sides: When Sirius realizes Pettigrew survived his betrayal of the Potters, he becomes obsessed with hunting him down and avenging them, nearly succeeding if it weren't for Harry interceding. Pettigrew sacrifices his living hand to bring Voldemort back, and is rewarded with a magical silver hand. In the seventh book, Pettigrew has a moment's hesitation (due to Harry saving his life four years prior) when carrying out Voldemort's orders, which is enough for the hand to strangle him.
- The fake Mad-Eye Moody claims he can't abide traitors, which is why he looks down on former Death Eaters like Karkaroff and Lucius Malfoy. He's even telling the truth: they're Death Eaters who escaped imprisonment by claiming they were Double Agents or mind-controlled, while Barty Crouch Jr. went to Azkaban along with other loyalists before escaping to serve Voldemort in disguise.
- In Harry Potter and the Order of the Phoenix, the curse Hermione gave to anyone ratting on Dumbledore's Army was a permanent marking on the face.
- Brother Cadfael: During the Forever War between Queen Maud and King Stephen, she sends her most trusted messenger with highly personal papers and jewelry to get help from her French relations, but the messenger is never seen again. Hugh Beringar looks for the murderer despite his fealty to Stephen, and is horrified to realize that the messenger never died, but took on another identity as a hermit until he could escape, murdering a man who could have recognized him and getting killed in turn. He calls off the search in disgust, and bears no grudge against Cadfael (who'd already figured it out) for letting the traitor's murderer get away.
- In Star Trek, the three pillars of Klingon philosophy are duty, honor, and loyalty. Officially, the Klingons play this trope straight.
- Worf does, but he's a particular case. Firstly, his parents died in a treacherous attack by the Romulans who had Klingon accomplices. Secondly, since he was adopted by human parents, he developed an idealized conception of the Klingon way of life.
- This aspect wasn't yet established during the original series, but the trope is still Played Straight by Kang. He has always scrupulously respected the Organian treaty, so he's pretty angry when his ship's disabled by what seems to be an unjustified attack from the Enterprise.
- Overall, a lot of treacherous Klingons appear onscreen. Sometimes, their strategy is accusing the adversary of treachery.
- In Klingon society, losing honor is officially worse than being killed and traitors are usually stripped of their honor.
- The episode "The Drumhead" starts with a Klingon who involved in espionage for the Romulans, but there's also the fight between Admiral Satie, who believes the end justifies the means to find imaginary traitors, and Picard, who points out that her methods betray the principles of Federation justice.
- In Lexx, Stanley Tweedle is known as the "Arch Traitor" (and hated enough by La Résistance that they're more willing to kill him than the Big Bad's guards) because...he got caught by some Space Pirates and gave away some security codes, after being tortured for them. Whenever it comes up, it's usually Played for Laughs.
- Babylon 5: Michael Garibaldi finds himself on both sides of this. At the end of the first season, he's shot In the Back by his second, Jack. When it comes to light, he goes to confront him, demanding to know why, and promising to be the one to push the button when Jack's Thrown Out the Airlock. In the fourth season, Garibaldi, who's been programmed by Bester's telepaths, arranges for Sheridan to be apprehended by Clark loyalists. When she hears about it, Ivanova orders Garibaldi shot on sight if he ever shows his face again.
- The Wire: In season 4, Randy Wagstaff, an eight-grade student in the Baltimore public school system, talks to the police after witnessing a murder perpetrated by the Stanfield drug gang. After word gets out, he is immediately targeted by his peers as a snitch, culminating in his house being firebombed and his foster mother permanently disfigured. Randy eventually has to go back to the badly-funded group home he already stayed in for years.
- Agents of S.H.I.E.L.D.: Even when there are wheels within wheels rolling and he holds many secrets (and understands other people have them), if there is a Berserk Button that will drive Phil Coulson up the wall immediately, is even thinking of stabbing the team in the back.
- In Angel, Wesley is manipulated into kidnapping Angel's son, Connor, believing Angel was going to eat Connor. This act of betrayal causes a big schism between the two and other members of the team. Not even having Wesley being in the hospital with his throat slit stopped Angel in attacking him. There's also a mention of Hell having a special place for traitors.
- In Firefly, Mal references the harsh punishments for traitors:
I hear how they used to keel-haul traitors back in the day. Now I don't have a keel to haul you on...
- The Bible:
Now the brother shall betray the brother to death, and the father the son; and children shall rise up against their parents, and shall cause them to be put to death.
- Judas's betrayal of Jesus, as recounted in The Four Gospels of The Bible. This betrayal was arguably necessary, as in Christian doctrine Jesus had to die to wash away mankind's sins, but Judas still has a My God, What Have I Done? moment followed by (in one account) a Driven to Suicide moment shortly thereafter.
- In Mark 13:12 this is considered a sign of the end of the world:
- God permitted the Hebrews to wage war, plant spies, and enslave for the sake of establishing themselves as a nation, but He condemned David for sending Uriah to his death so he could steal his wife.
- Warhammer 40K:
- Averted with Tzeentch, god of sorcerers, schemers and backstabbers, and his followers, for who betrayal at the worst possible time means everything is going Just as Planned.
- Khorne is the god of battle, rage and blood, and his followers don't consider it treason when they attack their own side (since blood spilled in battle strengthens Khorne). However, one of Khorne's greatest demons attacked him once (due to Tzeentch's manipulations), Khorne ripped his wings off and left him to slaughter for eternity without hope of being taken back.
- Every Imperial unit gets the Hatred special rule when fighting against gue'vasa (human auxiliairies serving in the Tau army). Willingly serving a xenos species is one of the highest forms of treason, never mind that some of them are descended from human worlds abandoned by the Imperium.
- Count Strahd von Zarovich's infamous Act of Ultimate Darkness from Ravenloft was the betrayal and murder of his brother Sergei on his wedding day so that he could have Tatyana, the woman both men loved, for himself.
- In Paranoia, all "commie mutant traitors" are to be immediately executed.
- Batman: Arkham City: Talia al Ghul is angry at Bruce and said him and her father deserve each other. Two minutes ago, she was the hostage of her own father. On the other hand, Bruce manipulated her because he needed Ra's al Ghul's blood to save a lot of lives. Of course, the al Ghul family doesn't have the same moral code as Batman.
- Sengoku Basara: Mitsunari Ishida's Berserk Button is betrayal. This is why he is intent on killing Ieyasu (for "betraying" and killing Hideyoshi) and why he considers anyone that defects from his army the lowest of scum.
- In Crusader Kings II, traitors can be freely imprisoned by their liege lord and can be striped of all their titles and then be banished, striping them of their gold to, without upseting any of your other vassals. To compare, murderers, rapists and homosexuals can only be imprisoned, with any other action against them leading to your vassals becoming majorly pissed. To be considered a traitor, a vassal must openly go to war with his liege lord and thus break his feudal oath. This made civil wars extremly gamey, as players could just annoy vassals whos titles they desired until they revolt and then just steamroll them. A patch then downplayed the traitor penalty, but it still is much harsher than any other punishment.
- In TIE Fighter, you serve under the Galactic Empire fighting the Rebel Alliance. Later in the game, the Alliance takes a backseat as you have to deal with two treacherous officers that need to face retribution, Admiral Harkov (defecting to the Rebels) and then Grand Admiral Zaarin (staging a coup against the Emperor).
- In Metal Gear Solid V: The Phantom Pain, the player can gas enemy soldiers, murder innocent animals, shoot your dog (though it'll always live,) and even develop a nuclear arsenal, but the evil the game prevents you from doing it shooting your own team mates.
- Star Fox: Pigma Dengar got his position in Andross' army on the basis of his betrayal of his partners James McCloud and Peppy Hare, resulting in the death of the former and the narrow escape of the latter. Even the other members of the Star Wolf team are disgusted by him.
- Command & Conquer: Tiberian Sun: After Anton Slavik is rescued by the other members of the Black Hand from his would-be execution by General Hassan (who is secretly on GDI's payroll), he returns to the bridge of his command ship and confronts the guy who sold him out. The traitor can barely get out a single line because Slavik shoots him on the spot. He's proud to engage in war crimes for the cause, but Slavik despises disloyalty with a fiery passion. He later publicly executes Hassan himself.
- Real Life Quote: MI-6 officer Nicholas Elliott confronting his former friend Kim Philby:
You took me in for years. Now I'll get the truth out of you even if I have to drag it out. You had to choose between Marxism and your family, and you chose Marxism. I once looked up to you, Kim. My God, how I despise you now. I hope you've enough decency to understand why.
- The Stop Snitchin' campaign was based on the idea that betraying your friends and comrades is worse than breaking the law.
- The international relations between France and the United States became colder in the 2000's because the French government vehemently opposed to a new war in Iraq (especially one under phony pretenses), which the Bush administration spun as betrayal.
- Being a delator (an accuser or informer) can be a fatal choice.
- The last execution in Britain happened in 1964. However, the United Kingdom totally abolished the Death Penalty in 1998. Treason was one of the last few offense punishable by death. It was already no more possible to be sentenced to death for murder since 1965 in England, Wales and Scotland and 1973 in Northern Ireland, but it was still possible for espionage until 1981.
- Vermont has no executed murderers since 1954 and abolished it on 1972, leaving only a maximum of life in prison for murder. However, they still have a mandatory death penalty for treason that no one took off the booksnote .
- In feudalism, disloyal vassals could be stripped from their fiefs without penalty.
- In some jurisdictions, being a traitor was so dishonorable even their descendants were said to have a tainted blood and couldn't inherit from him.
- During World War II, the government-in-exile of the occupied Norway expanded the use of the death penalty so that it would be easier to sentence people like Vidkun Quisling to death for treason. Keep in mind that pre-World War II, the last execution in Norway was in 1876. A quote by the prosecutor in the Court of Appeal case against Quisling:
Landsforræderi ansees med rette for den avskyeligste av alle forbrytelser fordi den kan bli så vidtrekkende og skjebnesvanger i sine konsekvenser, og fordi den underkjenner og angriper den samfølelse og det samhold som er en nasjons høyeste lov.
Treason is rightfully considered the most despicable of all crimes because it can be so far-reaching and fateful in its consequence, and because it invalidates and attacks the solidarity and unity which are the highest law of a nation.